#define _CRT_SECURE_NO_WARNINGS 1
#include<stdio.h>
int main()
{
	int ret=1;
	int n = 0;
	int sum = 0;
	scanf("%d", &n);
	for (int i = 1;i<=n;i++)
	{
		ret *= i;
		sum += ret;
	}
	printf("%d\n", sum);
	return 0;
}